The present invention relates to a multilayer resonance device for use in a device utilizing a magneto-optical effect and to a magneto-optical recording medium for recording/reproducing information through a magneto-optical recording/reproducing operation.
In the recent PC (personal computer) environment for dealing with dynamic image data, a magneto-optical recording medium, which has been widely used as a data recording device for a computer, is required to have a larger recording capacity, namely, there is a demand for a magneto-optical disk capable of high density recording. In order to increase a packing density, it is necessary to form short recording marks, but such short recording marks decrease a reproducing signal output due to waveform interference between the marks. Therefore, as a reproducing method for obtaining a reproducing signal without causing the waveform interference between the marks, various types of magnetically induced super resolution technique have been proposed. However, a magnetically induced super resolution medium has a structure including stacked layers of plural magnetic layers respectively having different magnetic characteristics, and hence, it is very difficult to control the magnetic characteristic and the exchange coupled force among the magnetic layers. Therefore, mass-production of such a medium is difficult. In addition, it is disadvantageously necessary to set recording/reproducing apparatus in accordance with the layer structure of the medium.
Furthermore, in a general magneto-optical disk, for example, in a magneto-optical disk having a structure including a SiN layer, a TbFeCo layer, another SiN layer and an aluminum layer successively stacked in this order on a substrate, an incident laser beam is made not to be reflected within the layers in order to attain a large magneto-optical effect. However, even in a magneto-optical disk using this non-reflection condition, it is impossible to obtain a Kerr rotation angle larger than one degree, and hence, such a disk is not suitable to reproducing short recording marks. Moreover, in a magneto-optical disk utilizing optics using evanescent light, that is, so-called near-filed optics, a reproducing signal output is so small that a medium for attaining a larger magneto-optical effect is demanded.
On the other hand, in the field of an optical isolator, a garnet monocrystal layer including YIG (yttrium-iron-garnet) as a main component is used, but the use is limited because light loss cannot be avoided. As a countermeasure, the present inventors and applicant have found that an optical isolator having a multilayer structure formed by alternately stacking a garnet monocrystal layer including YIG as a main component and a dielectric substance can attain a large magneto-optical effect and a high transmittance and can be free from light loss. Also, as a result of development of this finding, the present inventors and applicant have proposed a magneto-optical multilayer layer in Japanese Patent Application Laid-Open No.10-54965 (1998).
The magneto-optical multilayer layer disclosed in Japanese Patent Application Laid-Open No.10-54965 (1998) has a structure in which a magnetic substance and a dielectric substance are alternately stacked with their thicknesses irregularized, and can attain a very large magneto-optical effect. However, the number of stacked layers is large, and hence, the total thickness is large. Therefore, this magneto-optical multilayer layer is disadvantageously difficult to practically apply to a device utilizing a magneto-optical effect such as a microcavity and the aforementioned magneto-optical recording medium.